Reinforced catheter which gets softer towards the distal tip

ABSTRACT

The present invention comprises a catheter and method of manufacture. The catheter includes an elongated core having a unitary lubricous liner and a reinforcement. The lubricous liner defines at least one lumen. The lubricous liner has the reinforcement over the its outer diameter and fused to the lubricous liner. The reinforcement terminates proximal to the distal end of the lubricous liner. The catheter also has an elongated shaft tube which defines a shaft tube lumen. The shaft tube lumen is sized to receive the core, the core which extends longitudinally through the shaft tube lumen. The shaft tube is fused to the core. The catheter also has an elongated transition tube which defines a transition tube lumen. The transition tube lumen is sized to receive the core which extends longitudinally through the transition tube lumen. The distal end of the shaft tube is fused to the proximal end of the transition tube. The transition tube is made of softer material than the shaft tube and is fused to the core. The catheter further includes an elongated tip tube made of softer material then the transition tube. The tip tube defines a tip tube lumen sized to receive the core which extends longitudinally throughout the tip tube lumen. The distal end of the transition tube is fused to the proximal end of the tip tube. The tip tube is fused to the core distal to the distal end of the reinforcement, the distal end of the tip tube forming a rounded edge which overlaps the distal end of the lubricous liner by about 0.5 mm such that the distal end of the lubricous liner is not exposed.

This application is a continuation of application Ser. No. 08/368,186filed on Jan. 4, 1995 now abandoned.

FIELD OF THE INVENTION

The present invention relates to catheters, and more particularly, to amethod of soft tip attachment.

BACKGROUND OF THE INVENTION

Catheters are tube-like members inserted into the body for diagnostic ortherapeutic reasons. One of the therapeutic procedures applicable to thepresent invention is known as percutaneous transluminal coronaryangioplasty (PTCA). This procedure can be used, for example, to reducearterial build-up of cholesterol fats or atherosclerotic plaque.Catheters must have sufficient stiffness to be pushed through vessels aswell as sufficient rigidity to provide a high degree of torsionalcontrol. Stiffness or rigidity in the catheter tip poses the danger ofpuncturing or otherwise damaging a vessel as it twists through thevascular system. It is therefore desirable for catheters to have a softor flexible distal tip. Examples of such soft tip catheters are known inthe art.

The trend toward catheters with larger inside diameters and softerdistal tip segments results, however, in a substantially weaker bondbetween the soft tip and the distal catheter shaft because of thethinner wall thickness and lower tensile strength of the softermaterials. The following methods of tip attachment are known in the art.

Soft tips are often attached by means of a lap joint or butt joint atthe distal end of the catheter body where the soft tip has been fused orwelded to the catheter body. A butt joint or lap joint is undesirablebecause they create a stress concentration area at the distal end of thecatheter shaft in a plane perpendicular to the longitudinal axis of thecatheter shaft. The effect of this stress concentration is a low bondstrength between the catheter shaft and the soft tip when the wallthickness of the catheter shaft is less than 0.3 mm.

U.S. Pat. No. 4,596,563 to Pande for a "Thin-Walled Multi-LayeredCatheter Having a Fuseless Tip" discloses a two layered tubular bodyhaving a rigid inner sheath and a flexible outer sheath. The tip portionis fuseless with respect to the rest of the catheter, the tip portionbeing an integral extension of the flexible outer sheath that is formedover a gap between lengths of the rigid inner sheath.

U.S. Pat. No. 4,636,346 to Gold et al for a "Preparing Guiding Catheter"discloses a three-layered tubular body having a lubricous inner sheathdefining a lubricous guiding lumen, a rigid intermediate sheath and aflexible outer sheath. The distal tip portion has a similar constructionbut from which the rigid intermediate sheath is omitted. Col. 5, lines12-20 discloses a tip portion that may be an initially separate memberaffixed to the elongated tubular body 22 by suitable means, such as byheating, by other energy sources, and/or by adhesives or the like. Suchassembly can be assisted by the use of a length of shrinkable tubingthat is placed over the joint location prior to and during the assemblyoperation in order to enhance the smoothness and strength of the joint.It is an object of the invention to not require adding any braiding orstrands of strengthening material.

U.S. Pat. No. 4,863,442 to DeMello et al for a "Soft Tip Catheter"discloses a tubular body with a wire-braided Teflon® core and apolyurethane jacket. The distal end of the jacket is removed from thecore, and a soft polyurethane tip is applied to the core over the regionwhere the jacket has been removed. The tip overlaps the core forapproximately two millimeters and extends distally approximately twomillimeters beyond the distal end of the core. The tip may be applied tothe core as a separate tube bonded to it or be built up on the core byrepeatedly dipping the tip in a polyurethane slurry, or be molded ontothe distal end of the core. An embodiment at col. 5, lines 30-39discloses a sleeve of shrink film 64 placed over the polyurethane tube40 with the distal end of the jacket 18 and overlapping the shoulder 34.With the sleeve of shrink film 64 in place as shown in FIG. 2G, thedistal end of the assembly is heated to a temperature and for a timesufficient to cause the soft polyurethane tube 40 to flow and fill thegap 46 along with any other gaps which may exist between it and theshoulder 34, outer surface 36 of the core 16, and the outer surface 54of the mandrel 50.

U.S. Pat. No. 5,254,107 to Soltesz for a "Catheter Having Extended BraidReinforced Transitional Tip" discloses an embodiment in col. 4, lines34-41 wherein an inner tubular plastic layer 22 defines the innerdiameter of the catheter, and which extends through the first and secondsections 16, 18, but not through third tip section 20. Inner tubularlayer 22 may be made of PTFE. A braided stainless steel fiber tubularmember 24 surrounds inner plastic layer 22.

In the commonly owned, copending application of Brin et al. for"Improved Method of Catheter Segment Attachment" U.S. application Ser.No. 08/236,766 the distal end of the catheter consists of threesegments, the transition tubing which is attached to the shaft, the softtip tubing which is attached to the transition tubing, and the "plug"tubing which is attached to the soft tip tubing for ease of handlingduring manufacture and into which a support mandrel is inserted. Allthree segments are surrounded by a tube of heat shrink. The heat sourceacts upon the transition tubing with the heat being propagated to thesoft tip tubing. After assembly, the plug tubing and part of the softtip tubing are trimmed off. The catheter shaft is comprised principallyof three layers: a lubricous TEFLON® liner, a composite layer of wirebraid and polymer, and an outer jacket polymer. The wire braid andTEFLON® liner do not extend into the transition tubing or into the softtip tubing.

An object of the invention is to create a guiding catheter soft tip withwall thickness less than 0.3 mm which provides improved bond strength tothe catheter shaft joints, and in particular, the joint between the softtip segment and the segment proximal to the soft tip.

Another object of the invention is to provide a lubricious inner lumenthroughout the catheter body including throughout the soft tip whileshielding the lubricous liner from contact with the vessel wall andwhile maintaining a curved contour at the distal end.

Another object of the invention is to minimize the length of theunreinforced section of the soft tip to avoid devices snagging duringdeployment.

SUMMARY OF THE INVENTION

The present invention comprises a catheter and method of manufacture.The catheter includes an elongated core having a unitary lubricous linerand a reinforcement means. The lubricous liner defines at least onelumen. The lubricous liner has the reinforcement means over its outerdiameter and fused to the lubricous liner. The reinforcement meansterminates proximal to the distal end of the lubricous liner. Thecatheter also has an elongated shaft tube which defines a shaft tubelumen. The shaft tube lumen is sized to receive the core, the core whichextends longitudinally through the shaft tube lumen. The shaft tube isfused to the core. The catheter also has an elongated transition tubewhich defines a transition tube lumen. The transition tube lumen issized to receive the core which extends longitudinally through thetransition tube lumen. The distal end of the shaft tube is fused to theproximal end of the transition tube. The transition tube is made ofsofter material than the shaft tube and is fused to the core. Thecatheter further includes an elongated tip tube made of softer materialthen the transition tube. The tip tube defines a tip tube lumen sized toreceive the core which extends longitudinally throughout the tip tubelumen. The distal end of the transition tube is fused to the proximalend of the tip tube. The tip tube is fused to the core distal to thedistal end of the reinforcement means, the distal end of the tip tubeforming a rounded edge which overlaps the distal end of the lubricousliner by about 0.5 mm such that the distal end of the lubricous liner isnot exposed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is the preassembly plan view of the distal end of a guidingcatheter prior to the outer jacket molding process;

FIG. 2 is the molded assembly of FIG. 1;

FIG. 3 is the is a cross-sectional view of the distal tip of the moldedassembly of FIG. 2;

FIG. 4 is the plan view of the distal end of a guiding catheter prior tothe soft tip formation process;

FIG. 5 is the molded assembly of FIG. 4; and

FIG. 6 is a cross-sectional view of the distal tip of the moldedassembly of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention addresses the problem created by the trend towardcatheters with larger inside diameters and softer distal tip segments.Soft tip guiding catheters are desirable because the gentle ostialengagement is less traumatic. Soft tips provide a coaxial fit in allanatomies to allow for improved device delivery by maintaining a roundedtip shape which adapts to different ostial take-offs. Larger lumens aredesirable because they permit more dye flow and offer more devicedelivery options. The trend toward catheters with larger insidediameters and softer distal tip segments results in a substantiallyweaker bond between the soft tip and the distal end of the cathetershaft due to thin catheter shaft walls of less than 0.3 mm and to thelower tensile strength of the softer tip materials. Applicants addressthe problem of bond strength between segments and that of achievinggreater lumen lubricity by extending a unitary liner throughout theshaft, transition tubing and soft tip segments, the liner being made ofa fluoropolymer such as TEFLON® from E. I. Du Pont de Nemours & Company,Wilmington, Del. TEFLON® which is a form of polytetrafluoroethylene(PTFE). To maintain a soft tip, the TEFLON® is shielded from contactwith the vessel wall by using heat shrink tubing in a heating process todraw the distal end of the soft tip material over the exposed TEFLON®liner.

Manufacturing applicant's thin wall guiding catheter consists of twomajor processes, outer jacket molding and soft tip formation. FIG. 1-3,represent applicant's assembly for molding the outer jacket to thebraided TEFLON® core material. FIGS. 4-6 represent applicant's assemblyfor forming the soft tip.

Referring to FIG. 3 which depicts the molded assembly, the shaft of thethin wall guiding catheter for outer jacket molding is assembled asfollows. Slide the TEFLON® liner 40 over a stainless steel mandrel 30(not shown in FIG. 3). The mandrel 30 may optionally be TEFLON® coated.Next, braid wire 35 over the TEFLON® liner 40. The mandrel 30 has anouter diameter of approximately 0.001 inch less than the inner diameterof the TEFLON® liner 40. The mandrel 30 is used for support. TEFLON®beading could be alternatively used for support. After the cathetershaft is assembled, the support will be removed. The TEFLON® liner 40provides a lubricous surface which aids device delivery by providing alow friction interface. This is especially important for the smoothpassage of large, non-balloon devices which may not conform as readilyto guiding catheter curves. The TEFLON® 40 enhances device delivery withless device "capture" while ensuring circumferential integrity.

Wire 35 is braided by means of a conventional braiding machine over theTEFLON® liner 40 as shown in FIG. 3. The wire braid 35 is advantageousbecause it reinforces and supports the large lumen for thin wall guidingcatheters. The wire braid 35 is a 16 strand stainless steel braid whichruns the length of the catheter and is trimmed a few millimetersproximal to the distal end of the TEFLON® liner 40. The distal end ofthe wire braid 35 is then adhesively bonded to the TEFLON® liner 40.Those skilled in the art would recognize that other reinforcement meanscould be used, such as carbon fibers.

The catheter shaft comprises a plurality of segments overlying the wirebraid 35 and TEFLON® liner 40. These segments, the 72D shaft tubing 25,the 55D transition tubing 15, the 35D soft tip tubing 20 and the 72Dplug tubing 45 are made from PEBAX®. Although other polymers can befound in a suitable durometer range, PEBAX®, a polyether block amidecopolymer obtainable from the Elf Atochem Corporation, Philadelphia,Pa., is preferable in catheter design because it is an elastomer, haslow moisture absorbance, offers long term stability of materialproperties, provides high tensile strength and can be processed attemperatures in the 400 degree F range as required by commonly availableextrusion equipment. The segments are abutted as follows.

The shaft tubing 25 is made from PEBAX® in the hardness range of Shoredurometer D65-D75 and preferably 72D. The transition tube 15 may have ahardness range of Shore durometer 50D-60D and preferably 55D. Taper theend of the 72D Pebax® shaft tubing 25 using an outside taper cuttingtool. Cut a Shore 55D Pebax® transition tube 15 to 3.7 cm in length andtaper the end using an inside taper cutting tool. The 3.7 cm length waschosen from an acceptable range of 2 cm to 18 cm based on anatomicalconsiderations, as 4 cm is the average width of the aortic root. Slidethe untapered end of the Shore 72D shaft tubing over the braided TEFLON®liner 40 from its distal end. Next slide the 55D transition tubing 15onto the mandrel 30 and over the braided TEFLON® liner 40 from itsdistal end such that the tapered end of the 55D transition tubing 15mates with the tapered end of the 72D shaft tubing. The 72D shaft tubing25 and 55D transition tubing 15 can be tapered because the materials arestiff enough to retain their shape when melted. The material at thejoint will blend better when the mating ends are tapered yielding betterbond strength than would an abutted end as there is greater surface areaover which to blend the materials. The 55D transition tubing 15 may havea wall thickness of 0.013 inches (0.033 cm) and an inner diameterranging from a minimum of 0.078 inches for 6F to a maximum of 0.126inches for 10F. The wire braid 35 extends through the 55D transitiontubing 15 to offer better kink resistance and ends preferably atapproximately the proximal end of the 35D soft tip tubing 20 to permitmaximum flexibility in the soft tip 20. The wire braid 35 can stop from2-3 mm proximal to the 35D soft tip and still provide sufficientreinforcement but should not extend more than 1/3 of the length of thesoft tip 20 into the proximal end of 35D soft tip 20 to provide optimalsoft tip 20 flexibility. At least one inch of the mandrel 30 shouldextend beyond the distal end of the 35D tip tube 20 for ease ofhandling.

A softer durometer material is used for the soft tip 20 than for thetransition tubing 15 to give the distal end more flexibility; this aidsin tip placement. The soft tip 20 may be in the range of Shore 25D to40D and preferably 35D. The 35D tip tube 20 can be made of Pebax®. The35D tip tube 20 preferably has a length of approximately 1 cm prior totrimming and a wall thickness of 0.013 inches (0.33 cm) and an innerdiameter ranging from a minimum of 0.078 inches for 6F to a maximum of0.126 inches for 10F. The 1 cm length was chosen for handlingconvenience during the trimming process. Because the TEFLON® liner 40extends throughout all three segments (the 72D shaft tubing 25, the 55Dtransition tubing 15 and the 35D soft tip tubing 20) lubricity isimproved and device delivery enhanced. Furthermore, the unitary TEFLON®liner 40 extending throughout the shaft improves joint strength betweenthe 72D shaft tubing 25 and the 55D transition tubing 15 as well asbetween the 55D transition tubing 15 and the 35D soft tip tubing 20.

Slide a Shore 72D Durometer plug tube 45 of approximately 1 cm onto thedistal end of the mandrel 30 until it butts against the distal edge ofthe 35D soft tip tubing. The plug tube 45 can be made of Pebax®. Leaveapproximately 15.2 cm or 6 inches of mandrel 30 extending distallybeyond the assembly for handling convenience.

Slide a segment of TEFLON® fluorinated ethylene propylene (FEP) heatshrink tubing 10 over the entire assembly with approximately 1 cm ofheat shrink extending beyond the distal end of the 72D plug tube 45 andover the mandrel 30. Heat shrink tubing such as that from ZeusIndustrial can be used. Ensure that the joint between the 55D transitiontubing 15 and the 35D soft tip tubing 20 is approximately 15.9 cm fromthe distal end of the mandrel 30 for handling convenience.

The outer jacket is molded when the heat shrink 10 is heated by anysuitable means to fuse the segments. For example, radiant heating orconduction heating can be used. Heat shrink tubing 10 contraction, whencoupled with heating the tip materials causes them to expand, resultingin the materials blending and flowing into one another. A lap jointbetween the materials is produced. Those skilled in the art wouldrecognize that different time and temperature combinations would besuitable as time and temperature vary inversely.

To achieve bonding, the time and temperature selected must be sufficientto render the materials flowable. Temperatures which are too high willresult in a brittle product. Temperatures which are too low will resultin improper fusion. A suitable convection oven temperature for outerjacket molding includes 185 degrees centigrade. This temperature shouldbe maintained for approximately 7 to 8 minutes depending on the sizecatheter being molded. Those skilled in the art would recognize thatdifferent time and temperature combinations would be suitable as timeand temperature vary inversely. Referring to FIG. 2, the heat sourcecauses the catheter shaft tubing 25, the transition tubing 15, the softtip tubing 20 and the plug tubing 45 to become flowable while the heatshrink 10 contracts both radially and longitudinally thereby collidingall segments. This results in a lap joint between each segment.

The heat shrink tubing 10 is removed with a razor blade and the moldedtip assembly is cut to length. The distal end is trimmed back to a pointwithin the 35D soft tip tubing to result in a tip length of 2.5 mmdistal to the 55D transition tubing 15. Lengths that are much longer areundesirable because the soft tip 20 is not structurally rigid and mayfold back upon itself and cause difficulty with device passage. Themandrel 30 is removed from the inside of the now bonded assembly. FIG. 3shows the enlarged longitudinal cross section of the distal end portionof the molded assembly of FIG. 2.

After outer jacket molding, the soft tip 20 is formed. Extending theTEFLON® liner 40 to the distal end of the soft tip tubing improveslubricity. The unitary liner also improves joint strength between the35D soft tip 20 and the 55D transition tubing 15 but results in a tipthat is too sharp. To remedy this, a soft tip 20 tapered distal edgewhich overlaps and shields the TEFLON® liner 40 and can be created asfollows to blunt the sharp TEFLON® liner 40. See FIG. 4. Taking theassembly from the outer jacket molding process, insert a mandrel 30 intothe distal end of the assembly such that at least 1 inch protrudes fromthe distal tip of the assembly. Apply approximately 2 inches of heatshrink tubing 110 over the distal end of the assembly such that the heatshrink 110 extends one-half to one centimeter beyond the proximal anddistal ends of the soft tip 20 material as seen in FIG. 4. Next insertthe assembly (until the soft tip 20 material can no longer be seen) intoa preheated forming die, as for example, a hot block consisting of abrass cylinder with and external band heater. Dwell at a temperature of400 degrees F. This temperature is maintained for approximately 7 to 8seconds depending on the size catheter being molded. Those skilled inthe art would recognize that different time and temperature combinationswould be suitable as time and temperature vary inversely. Remove theassembly from the forming die. The heat shrink 110 will have contractedabout the soft tip 20 as seen in FIG. 5. After the assembly has cooledfor at least 10 seconds, remove the heat shrink tubing 110. Remove thesupporting mandrel 30. As seen in FIG. 6, the contraction of the heatshrink 110 will have caused the 35D soft tip 20 material to flow anddraw the distal end of the 35D soft tip 20 approximately 0.5 mm over thedistal end of the TEFLON® liner 40, thereby covering the exposed TEFLON®liner 40 by creating a somewhat radiused, overhanging edge 65.

Applicants reinforced soft tip 20 with an unreinforced rounded edge 65is advantageous. A rounded edge 65 shielding the exposed TEFLON® liner40 reduces trauma in body cavities. It is common to deliver such devicesas balloon catheters, stents or atherectomy devices through guidingcatheters. Having a short unreinforced soft tip edge 65 of 0.5 mm isadvantageous because it diminishes the likelihood of devices snaggingduring device delivery. Soft tips on guide catheters deflect easily,especially if they are unreinforced. Unreinforced soft tips of two mm ormore increase the likelihood of devices snagging during delivery.Unreinforced soft tips of less than 1 mm reduce the likelihood of adevice snagging. Applicant's soft tip 20 having the TEFLON® liner 40throughout the soft tip 20 provides increased stiffness which furtheravoids devices snagging during deployment.

The preceding specific embodiments are illustrative of the practice ofthe invention. It is to be understood, however, that other expedientsknown to those skilled in the art or disclosed herein, may be employedwithout departing from the spirit of the invention or the scope of theappended claims.

    ______________________________________                                        No.             Component                                                     ______________________________________                                        10              Heat Shrink Tubing                                            15              55D Transition Tubing                                         20              35D Soft Tip Tubing                                           25              72D Shaft Tubing                                              30              Mandrel                                                       35              Wire Braid                                                    40              TEFLON ® Liner                                            45              72D Plug Tube                                                 50              Shaft Tube Lumen                                              55              Transition Tube Lumen                                         60              Tip Tube Lumen                                                65              Rounded Edge                                                  110             Heat Shrink Tubing                                            ______________________________________                                    

What is claimed is:
 1. A catheter comprising:an elongated core having aunitary lubricious liner and a wire braid reinforcement means, the wirebraid reinforcement means having a proximal end and a distal end, thelubricious liner having a distal end, an outer diameter and a proximalend, the lubricious liner defining at least one lumen, the lubriciousliner having the wire braid reinforcement means over the outer diameterand fused to the lubricious liner; an elongated shaft tube having adistal end and a proximal end, the shaft tube defining a shaft tubelumen, the shaft tube lumen being sized to receive the core, the coreextending longitudinally through the shaft tube lumen, the shaft tubebeing fused to the core; an elongated transition tube having a distalend and a proximal end, the transition tube defining a transition tubelumen, the transition tube lumen being sized to receive the core, thecore extending longitudinally through the transition tube lumen, thelubricious liner having the wire braid reinforcement means over theouter diameter and fused to the lubricious liner throughout thetransition tube, the distal end of the shaft tube being fused to theproximal end of the transition tube, the transition tube being fused tothe core, the transition tube being made of softer material than theshaft tube; and an elongated tip tube having a distal end and a proximalend, the tip tube being made of softer material than the transitiontube, the tip tube defining a tip tube lumen, the tip tube lumen beingsized to receive the lubricious liner and the wire braid reinforcementmeans, the distal end of the transition tube being fused to the proximalend of the tip tube, the lubricious liner and the wire braidreinforcement means extending through the proximal end of the tip tube,the wire braid reinforcement means terminating proximal to the distalend of the tip tube, the lubricious liner extending substantially thelength of the tip tube, the distal end of the tip tube being drawndistally over the distal end of the lubricious liner so that the tiptube is structurally secured to at least one of the lubricious liner andthe wire braid reinforcement means over substantially the length of thetip tube.
 2. The catheter of claim 1 wherein the distal end of the tiptube curves over the distal end of the lubricious liner to define anunreinforced rounded edge of the tip tube and wherein the lubriciousliner provides structural reinforcement along the length of the catheterincluding substantially throughout the tip tube to minimize the lengthof the unreinforced rounded edge of the tip tube and to avoid snaggingduring deployment.
 3. The catheter of claim 2 wherein the rounded edgeextends approximately 0.5 mm distally beyond the lubricous liner.
 4. Thecatheter of claim 1 wherein the shaft tube is made from a polymermaterial exhibiting a hardness in the range of Shore durometer 65D to75D.
 5. The catheter of claim 1 wherein the transition tube is made froma polymer material exhibiting a hardness in the range of Shore durometer50D to 60D.
 6. The catheter of claim 1 wherein the tip tube is made froma polymer material exhibiting a hardness in the range of Shore durometer25D-40D.
 7. The catheter of claim 1 wherein the shaft tube distal endand the transition tube proximal end have complimentary tapers.
 8. Thecatheter of claim 1 wherein the lubricous liner is made of afluoropolymer material.
 9. The catheter of claim 1 wherein at least onecomponent is selected from a group consisting of the shaft tube, thetransition tube and the tip tube is made from a polyether block amidecopolymer material.
 10. The catheter of claim 1 wherein the distal endof the wire braid reinforcement means extends into the proximal end ofthe tip tube for not more than one third of the length of the tip tube.11. The catheter of claim 1 wherein the transition tube has a length ofapproximately 3.7 cm.
 12. The catheter of claim 1 wherein the tip tubehas a length of approximately 2.5 mm.